In many applications, such as graphic arts production, it is important that the colors in a printed document match the colors that were desired or expected when the document was created. The expectation may be based on the CRT monitor representation, or based on specifications found in swatch books or embedded within integrated circuits. Ideally, all of the colors in the document would be contained within the “device colors” of the printing device, where device colors are the range of colors accurately processed by a particular device without resorting to color mapping. Unfortunately, containment of a document within the device colors is rarely realized. This is particularly true for subtractive ink-and-media printing systems, which have less color range than most input devices such as scanners or additive output devices such as CRT monitors.
The color gamut of a typical CRT monitor far exceeds that of a printer. Some exceptions may be found in the extreme yellow and cyan-green areas where a printer may have slightly more color range than many monitors. Nevertheless, it follows that a document composed on a monitor may contain colors that cannot be reproduced on a printer. This condition can result in mismatches between the composed document and the printed document.
One way to solve this problem is to limit the colors in the composed document to those colors reproducible by a given printer. This is often not practical, however, since the printer gamut information is not always available. This method also makes the document device-specific and non-portable. A document created in this fashion could not be printed satisfactorily on other printers with different color gamuts, and would have a color space that would appear limited when viewed with a CRT monitor. This would negatively impact documents also used in Internet applications.
A second way to solve the problem is to employ a gamut mapping algorithm. Gamut mapping is a process by which the colors found within a document to be printed are converted by a mapping process into a printer's device colors. Thus, a printer's color gamut would include the printer's device colors, as well as colors that could reasonably be mapped to device colors. Therefore, gamut mapping increases the ability of printers to print documents having a diverse color gamut.
Unfortunately, no gamut mapping algorithm is without drawbacks. As a result, several competing gamut-mapping strategies have relative merits. Each is based on satisfying differing “rendering intents” of the document's author. For example, the rendering intent may be accuracy. In this case, colors within the document that are also within the printer's device colors are reproduced unchanged; other colors are mapped as little as possible to bring them within the printer's device colors. Alternatively, the rendering intent may be perceptual. In this case, colors not within the printer's device colors are mapped onto device colors, and colors within the printer's device colors are mapped to other device colors, thereby preserving some of the relative spacing between colors. Such a strategy tends to preserve the perception of color transitions, but is less successful at preserving accuracy.
A related problem may result where the region corresponding to the device colors of a printer exceed the requirements of a document to be printed. In this case, the gamut mapping may needlessly and automatically be employed, resulting in undesired gamut compression.
In view of the above limitations, printers' generalized gamut mapping algorithms tend to result in color errors related to accuracy, perception and combinations of both. Accordingly, it would be beneficial to develop a document-to-printer color gamut matching system that provides a better match between the color gamut requirements of a document and the color gamut space of a printer.